diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index b9b6bd96..c8c08f19 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -40,7 +40,6 @@ jobs:
           - { os: ubuntu-latest  , ruby: truffleruby-head }
         exclude:
           - { os: windows-latest, ruby: jruby }
-          - { os: windows-latest, ruby: jruby-head }
 
     steps:
       - uses: actions/checkout@v5
diff --git a/.github/workflows/sync-ruby.yml b/.github/workflows/sync-ruby.yml
new file mode 100644
index 00000000..29c43449
--- /dev/null
+++ b/.github/workflows/sync-ruby.yml
@@ -0,0 +1,33 @@
+name: Sync ruby
+on:
+  push:
+    branches: [master]
+jobs:
+  sync:
+    name: Sync ruby
+    runs-on: ubuntu-latest
+    if: ${{ github.repository_owner == 'ruby' }}
+    steps:
+      - uses: actions/checkout@v5
+
+      - name: Create GitHub App token
+        id: app-token
+        uses: actions/create-github-app-token@v2
+        with:
+          app-id: 2060836
+          private-key: ${{ secrets.RUBY_SYNC_DEFAULT_GEMS_PRIVATE_KEY }}
+          owner: ruby
+          repositories: ruby
+
+      - name: Sync to ruby/ruby
+        uses: convictional/trigger-workflow-and-wait@v1.6.5
+        with:
+          owner: ruby
+          repo: ruby
+          workflow_file_name: sync_default_gems.yml
+          github_token: ${{ steps.app-token.outputs.token }}
+          ref: master
+          client_payload: |
+            {"gem":"${{ github.event.repository.name }}","before":"${{ github.event.before }}","after":"${{ github.event.after }}"}
+          propagate_failure: true
+          wait_interval: 10
diff --git a/CHANGES.md b/CHANGES.md
index 747b8059..1f0b7873 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -2,10 +2,14 @@
 
 ### Unreleased
 
+### 2025-10-07 (2.15.1)
+
+* Fix incorrect escaping in the JRuby extension when encoding shared strings.
+
 ### 2025-09-22 (2.15.0)
 
 * `JSON::Coder` callback now receive a second argument to convey whether the object is a hash key.
-* Tuned the floating point number generator to not use scientific notation as agressively.
+* Tuned the floating point number generator to not use scientific notation as aggressively.
 
 ### 2025-09-18 (2.14.1)
 
diff --git a/java/src/json/ext/SWARBasicStringEncoder.java b/java/src/json/ext/SWARBasicStringEncoder.java
index 02a3bfcd..a6695d99 100644
--- a/java/src/json/ext/SWARBasicStringEncoder.java
+++ b/java/src/json/ext/SWARBasicStringEncoder.java
@@ -27,9 +27,10 @@ void encode(ByteList src) throws IOException {
         // slice a string, the underlying byte array is the same, but the
         // begin index and real size are different. When reading from the ptrBytes
         // array, we need to always add ptr to the index.
-        ByteBuffer bb = ByteBuffer.wrap(ptrBytes, ptr, len);
+        ByteBuffer bb = ByteBuffer.wrap(ptrBytes, 0, ptr + len);
+
         while (pos + 8 <= len) {
-            long x = bb.getLong(pos);
+            long x = bb.getLong(ptr + pos);
             if (skipChunk(x)) {
                 pos += 8;
                 continue;
@@ -48,7 +49,7 @@ void encode(ByteList src) throws IOException {
         }
 
         if (pos + 4 <= len) {
-            int x = bb.getInt(pos);
+            int x = bb.getInt(ptr + pos);
             if (skipChunk(x)) {
                 pos += 4;
             }
diff --git a/lib/json/version.rb b/lib/json/version.rb
index e2db923e..be5daf4c 100644
--- a/lib/json/version.rb
+++ b/lib/json/version.rb
@@ -1,5 +1,5 @@
 # frozen_string_literal: true
 
 module JSON
-  VERSION = '2.15.0'
+  VERSION = '2.15.1'
 end
diff --git a/test/json/json_encoding_test.rb b/test/json/json_encoding_test.rb
index 8dce81da..2789e94b 100644
--- a/test/json/json_encoding_test.rb
+++ b/test/json/json_encoding_test.rb
@@ -35,6 +35,8 @@ def test_generate_shared_string
     # Ref: https://github.com/ruby/json/issues/859
     s = "01234567890"
     assert_equal '"234567890"', JSON.dump(s[2..-1])
+    s = '01234567890123456789"a"b"c"d"e"f"g"h'
+    assert_equal '"\"a\"b\"c\"d\"e\"f\"g\""', JSON.dump(s[20, 15])
   end
 
   def test_unicode